Means for receiving weak signal currents



April 7, 1925/ 1,532,172

J. R. CARSON mums FOR RECEIVING WEAK new, CURRENTS Filed June 1a, 18

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JOZmR 62713014 BY Z f4) E ATTORNEY Patented Apr. 7, 1925.

UNITED STATES PATENT OFFICE.

JOHN B. CARSON, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MEANS FOR RECEIVING WEAK SIGNAL CURRENTS.

Application filed June 18,

To all whom it may concern:

Be it known that I, J OHN R. CARsoN, residing at New York, in the countyof New York and State of New York, have invented certain Improvements inMeans for Receiving Weak Signal Currents, of which the following is aspecification.

This invention relates to signal transmitting systems and especially totelegraph systems involving transmission lines of large distortion andattenuation, such as are found in ocean cable work. The object of theinvention is to improve the quality and speed of transmission over suchlines.

In lines of the character mentioned, it is a matter of common knowledgethat the speed of signaling is much limited by the losses in the lineand the distortion of the current impulses and various schemes have beenproposed for. overcoming these difiiculties. It has recently beenproposed to combine a distortion network having a corrective effect uponthe received impulses and a distortionless amplifier, such as thethermionic type, with transmission lines of this kind, and it has alsobeen suggested that the correcting networks of the amplifiers may beused in stages alternately. These suggestions have originated withothers and in" themselves form no part of the present invention. It isthe purpose of this invention to provide a correcting network of anespecially efiicient form for use in connection with the amplifyingelements.

The invention will be described in connection with the accompanyingdrawing in which Figure 1 illustrates diagrammatically one end of asignaling system embodying the invention; Fig. 2 is a set of curvesillustrating the operation of the invention, and Fig. 3 shows curvesrepresenting the results obtainable.

The terminal of the main line 1, here represented as a cable circuit,may be connected to one winding 2 of a transformer 3, the other sideofthis winding being connected to the artificial line 4, commonly used forduplex operation. The other winding 5 of the transformer will then beconnected to the apparatus in the receiving branch of the circuit andthe sending apparatus will be connected between a lead 6 tapped in atthe center point of the winding 2 and ground. It will be understood, ofcourse, that any other 1918. Serial N0. 240,631.

common means for deriving the sending and receiving branches for duplexoperation may be employed.

In the form of the invention here illustratcd, I have shown an amplifier7 connected immediately to the terminals of the transformer winding 5with the input side next to the transformer and the output sideconnected to a correcting network arranged in accordance with thisinvention. It will be understood, however, that, if desired, thecorrecting network may be connected directly to the transformer windingand the amplification accomplished at subsequent stages. The correctingnetwork comprises an inductance 8, resistance 9 and capacity 10,connected across the circuit, the capacity being shunted by a resistance11 which co-operates with the capacity for the purpose hereinafterpointed out and at the same time provides the proper circuit for the Bbattery of the amplifier. The plate circuit of the amplifier ispreferably connected somewhere between the ends of the inductance 8 togive an auto-transformer operation thereto which facilitates voltage adustments in the successive stages of the apparatus. In general thevoltage should be stepped up between stages. The total value ofinductance 8 as Well as the relative value of the parts on either sideof the connection to amplifier 7 must be proportioned With a view to thedesired correcting effect as well as the desired step up in voltage.

The current arriving over the line 1, when the distant end is closedthrough a source of currents and held closed, may be represented by thecurve a'in Fig. 2. The effect of the transformer 3 will be to give inthe amplifier circuit only a current approximating the first derivativeof this arrival current which may be represented by the curve'b in Fig.2. The effect of the inductance 8 in the correcting net-work is to givea second derivative represented by c in Fig. 2, while the resistance 9maintains the first derivative or b. By inserting the capacity 10 in themanner here shown, the integral of the first derivative, which is thesame as the arrival curve a, may be approximately obtained. It will beobvious from an inspection of Fig. 2 that if the curves a, b and c aregiven proper values that their combined effect will be a current curvehaving a fairly sharp rise side of an amplifier 8, as shown. To

ployed. The thermionic amplifier serves the purpose in hand because itcan be made practically distortionless, thus avoiding there-introduction of the defects which have been eliminated. The amplifieralso serves an important function in preventing the networks fromreacting upon one another so that each may be independently designed tohave its desired effect. This results from the fact that the amplifieris a one-way device. The output side of the distortion net work is,therefore, connected to the input prevent the B battery of amplifier 7from affecting the potential between grid'and filament of amplifier 8',the condenser 12 is inserted, and a resistance 13 is bridged across theinput circuit of the latter to permit of a proper control of potentialdifference between grid and filament in the latter amplifier. Thecondenser 12 and resistance 13 constitute no part of the correctivenetwork and in*order that they may not affect the action thereof theresistance 13 should be of very high value compared with the impedanceof the network. The condenser 12 should also beof large capacity so asnot to affect the signaling voltage in the input circuit of amplifier 8'Improved results are obtained by repeating the correction andamplification of the current through successive stages as indicated at14 and 15. The number of stages and the values of the various elementsof the distortion network will depend upon the character of thetransmission line with which they operate. Curve X in Fig. 3 representsthe current which may be obtained from an arrival current such asindicated at a in Fig. 2 by the use of two stages of the network withamplifiers intervening as shown in Fig. 1. Curve Y shows the resultswith three stages, which is a considerable improvement over X since itshows a sharper rise and a flatter top.

The invention is not to be regarded as limited to the details of thecircuit arrangements herein shown as various modifications will suggestthemselves to those skilled in the art within the spirit of theinvention and the scope of the appended claims.

WVhat is claimed is: 1. The combination with a main line havingdistortion and attenuation, a correctoperating with said transformer toreform said signal impulses, said network comprising an inductanceelement receiving current through part of its coils and transmittingcurrent through all of its coils whereby the voltage of the outputcircuit of said network may be increased.

3. The combination with a line of high distortion and attenuation, of atransformer receiving signal impulses therefrom, an amplifier having itsinput circuit connected across the secondary of said transformer, adistortion circuit connected across the output circuit of said amplifierand comprising inductance, resistance and capacity arranged in series, asecond amplifier receiving impulses from said distortion circuit andmeans between the distortion circuit and said second amplifier formaking the input circuit of the second amplifier of high impedance.

4. The combination with a signaling conductor having distortion andattenuation, of a wave shaping network, comprising a step-upauto-transformer, a resistance in series with the primary portion ofsaid transformer in the primary circuit and also in series with thesecondary portion in the secondary circuit, and means for impressingupon the primary circuit signal waves having components of very lowfrequencies.

5. The combination with a submarine telegraph cable having distortionand attenuation, of a wave shaping network comprising anauto-transformer, primary and secondary circuits therefor, a resistancecommon to said circuits, a space discharge amplifier of high impedancein said output circuit, and means for impressin upon said input circuitsignal waves having very low frequency components.

In testimony whereof I have signed my name to this specification this17th day of June, 1918.

JOHN R. CARSON.

